1. Field of the Invention
The present invention relates to compression ignition internal combustion engines including exhaust gas recirculation and variably operating between an exhaust gas recirculation mode and a boost mode, wherein an engine control monitors operating conditions to limit exhaust gas recirculation when operating conditions would permit condensation in the intake manifold and automatically reentering exhaust gas recirculation mode when the condensation conditions are alleviated.
2. Background Art
Condensation is a problem identified in engines using Exhaust Gas Recirculation (EGR). The hot exhaust gas from diesel engines includes a mixture of water vapor from the burnt fuel and ambient air. EGR engines recirculate a limited amount of exhaust gas back into the intake manifold to combust any unused fuel and byproducts. Due to the lower temperature of the intake air at the intake manifold, condensation may occur in the manifold when exhaust gas is mixed with fresh air in the intake manifold. For a given operating condition (with fixed air/fuel ratio (AFR), the variable degree of recirculation (% EGR) and intake manifold pressure (IMP)) and for a given ambient conditions such as ambient temperature (ATI) and relative humidity (ATIRH), the water vapor will condense at a dew point temperature. The dew point temperature is defined as the Intake Manifold Critical temperature (IMT_Critical). The condensate is acidic due to presence of compounds of Nitrogen and Sulfur from fuel. Nevertheless, the engine and the equipment in which it may be installed operate in wide ranges of ambient temperatures, for example, −25 deg C. to 50 deg C. and relative humidity 0% to 100%, for highway.
In a known engine control, when the measured Intake Manifold Temperature (IMT) becomes less than or equal to IMT_Critical, the engine control has been programmed to go into condensation mode and turn off EGR. Once EGR is turned off, the engine is running in a mode without exhaust gas recirculation. This operation is called the Boost mode. A timer then governs when the control pushes the engine back into the EGR mode. An IMT_Critical calculation is performed to validate the stay in EGR mode. If IMT is found to be below IMT_Critical, then EGR would be turned off. Once the engine is in Boost mode, previous controls do not and can not detect if condensation would occur when the EGR is turned on. Accordingly, unnecessary modes and transitions may be repeated. With the current strategy, the engine is stuck running in boost mode until the timer comes into effect even if the speed and load conditions of the vehicle change due to various reasons.